Heat-copying process



HEAT-COPYING PROCESS Filed 001'.. 19. 1961 Jaz/rae reas 7 F'G. 4 Jl Paw/er Ima e #fte/- Remawwy 7 q Master fina Car/faena; 77;@

INVENTOR. .E7-wz?? Iz/'17d United States Patent O M' 3,196,029 HEAT-CGPYNG PROCESS Erwin Lind, Wiesbaden-Biehrich, Germany, assignor to Kalle Aktiengesellschaft, Wiesbaden-Biebrich, Germany Filed Oct. 19, 1961, Ser. No. 145,323 Claims priority, application Germany, Dec. 10, 1960, 42,365; Dec. 27, 1960, K 42,512; Jan. 7, 1961, K 42,531

27 Claims. (Cl. 117-15) The present invention relates to a heat-copying process in which a layer of a hat-sensitive natural, modified natural or synthetic resin is exposed to a heat image and then developed by treatment with a developer. The developed image may be fixed if desired.

Copies have been prepared by the image-wise action of heat on a material which, when heated, becomes discolored as a result of chemical reaction. Copies hitherto obtained in this way have the disadvantage that they discolor completely when unintentionally heated and thus become unusable. Moreover, they are not permanent when exposed to light, hence, such copies are unsuitable for use as documents. ln another known heat-copying process, a colored Wax is transferred by image-wise heat action to a copy support. The copies obtained by this process, however, lack adequate definition.

The present invention provides a heat copying process which comprises effecting image-wise exposure to radiant heat of a surface Vconsisting of a heat-sensitive natural or synthetic resin, or a heat-sensitive modified natural resin, and thereafter developing the latent heat image formed on the surface, to render it visible, by treatment with a colorless or colored powder, followed by xing of the developed image, where necessary.

The invention will be further illustrated by reference to the accompanying drawings in Which- FEGURE l shows an arrangement of a master and a heat-sensitive resin layer as employed during the Contact copying process,

FGURE 2 shows an arrangement of a master and a heat-sensitive resin layer as employed in the reflex copying process, and

FIGURES 3 and 4 show a powder image formed on the heat-sensitive resin layer after removing the master and contacting the heat-sensitive resin layer with powder.

The synthetic resins suitable for use in the process according to the invention normally have a softening temperature between 40 an-d 180 C., but, in some special cases, synthetic resins having a softening temperature below or above these limits are suitable.

The syntheic resin may be a polyamide, eg. a polymer of an w-aminocarboxylic acid or a lactam thereof or condensatioa product or mixed condensation product of a diamine and a dicarboxylic acid. Very favorable results are obtained with polycaprolactam and with a condensation product of adipic acid and hexamethylene diamine. Polyamides containing substituents, particularly allroxymethyl groups, attached to the carbonamide nitrogen atoms are particularly suitable. The substituent alkoxymethyl groups may be introduced into the polyamides by heating a solution of the polyamide in formic acid or acetic acid with formaldehyde and the appropriate alcohol, eg. methanol, ethanol or propanol. According to the proportions used, polyamides are obtained in which 3,196,629 Patented July 20, 1%65 ICC the hydrogen atoms on the carbonamide nitrogen atoms are replaced by alkoxymethyl groups to varying degrees. As the sensitivity of the polyamide to radiant heat increases With increasing substitution, it is preferred to use polyamides which are fairly highly substituted. Those in which about 30 to 60% of the hydrogen atoms on the carbonamide nitrogen atoms are replaced by alkoxymethyl groups are particularly suitable. Polyamides with greater or lesser substitution can be used, but with polyamides with less substitution the time required for exposure increases.

As an alternative to the use of a polyamide, the synthetic resin may be another thermoplastic resin, e.g. a polyvinyl compound such as polyvinyl chloride, chlorinated polyvinyl chloride, polyvinyl acetate, polystyrene and modified polystyrene, a polyole'fin, preferably polyethylene or polypropylene, an interpolymer or polymer mixture derived from these substances, a polyester, e.g. polyterephthalic acid ester or an interpolymer of terephthalic acid and isophthalic acid with ethylene glycol, a polyacrylic compound such as polyacrylic acid ester or a polyhalogenated hydrocarbon, such as a diphenyl chloride resin. Preferably, the resin has a softening point (Krmer-Sarnow-Nagel) of 6ft-70 C., a color number of 1 2 and an acid number of 0'.

Natural resins suitable for the process according to the invention are, primarily, shellac and colophony. Very favorable results are also obtained with modified natural resins, i.e conversion or refinement products, e.g. hydrogenated resins such as dihydroand tetra-hydroabietic acid, zinc resins, e.g. the product commercially available as Erkazit-Hartharz (melting point: 15S-130 C.) and polymerized resins, e.g. the product commercially available as Polypale Resin (melting point: 9S-106 C.).

The synthetic resin may also be a thermosetting resin, for example an ester resin such as a maleinate resin, c g. a modified maleic acid resin having a melting point of 60-70" C. and an acid number of 1Z0-130, or the product commercially available as Hobimal P (melting point: ISO-158 C.), a phenolic resin such as a novolak, e.g. the product commercially available as Alnovol 429K (melting point: 10S-118 C.), or a non-plasticized phenol resin of the resol type having a melting point Vof L15-58" C., a modified phenolic resin, e.g. a phenolic resin modified with colophony and having a melting point of 59-65 C. and an acid number of about 80, a phenolic resin modified with resin acid or resin acid esters, eg. the product commercially available as Albertol 3 69a (melting point: 1Z0-130 C.), a ketone resin, e.g. a ketone resin having a melting point of 76-82" C., a color number of 1-2.5, and a saponification number of 0, or a ketoneformaldehyde resin having a softening temperature of 11S-120 C. and an acid number of 0.

The compounds specified, particularly the colorless alkoxymethylated polyamides, can be used in the form of self-supporting foils or in the form of a thin coating applied to one or to both sides of a support. A wide range of materials can be used for the support, which is preferably in the form of a flat sheet or foil. Paper, cellulose hydrate, plastic or metal foils, for example, are very suitable. Rigid supports made of glass or pottery are, however, also suitable.

To prepare an image from a master, the copying material is exposed to radiant heat. This can be done by the contact method, .as illustrated in FIGURE l of the drawings, when the master has text on one side only, in which case the infra-red radiation from a radiant heat source 4 pass through the master l, having the printed matter 2 thereon, to the heat-sensitive resin layer 3 in which the heated areas 6l are formed or by the reflex method in the case of a master having text on both sides, as shown in FIGURE 2 of the accompanying drawings, in which case infra-red radiation 5 from the radiant source 4 passes through the copying material, i.e., the heat-sensitive resin layer 3a which is placed between the radiant .source 4 and a master lla for reflex copying, which has the printed matter 2 thereon, with the result that the "heated areas 6 are formed in the heat-sensitive resin layer 3a. The radiant'heat is absorbed in the image parts of the master and converted into perceptible heat which produces on the copying material a latent image corresponding to the master. This latent image persists for at least several minutes after the removal of thefsource of heat. The durationfof the exposure to heat, needed for the formation of the latent image, depends on the sensitivity of the copying material and on the intensity of heating; however, the copying material should not normally be heated to a temperature above the softening point of the resin. FIGURES 3 and 4 show the powdered image areas 7 formed on the heat-sensitive resin layer 3 used in the contact copying process and on the resin layer 3a used in the reex copying process after removing the master in each case and'contacting the heat-sensitive resin layers with developer powder. In order to obtain the sharpest possible image, the master and the c-opying material shouldv be in the closest possible contact and the exposure to heat should be as brief and intensive as possible. The thickness of the resin coating applied to the support is generally between about l and 50p, preferably between about 3 and 10u. Commercially available infra-red radiators, e.g. of from 1000 to 2000V watts, or an infra-red flash may be used as the source of heat. The process can be performed in a machine in which the copying material passes, in close contact with the original, over rollers at a speed of several meters a minute through the focal point of a focused 1350-watt infra-red radiator.

It it also possible by the present process to produce positive copies from negative originals. To achieve this, the resin-coated side of the copying material is covered with a cellulose acetate lm having a thin silver coating, e.g. an exposed, developed and fixed photographic film, which is placed with the silver coating in contact with the heat-sensitive coating of the copying material, and the infra-red radiation is passed through the master and the cellulose acetate iilm. The heat produced by the absorption of the infra-red rays in the master is prevented by the cellulose acetate film from passing to the heat-sensitive coating of the-copying material. radiation which passes through the negative master is however absorbed by the silver coating. As the result of the contact of the latter with the heat-sensitive coating a positive latent image is formed on the heat-sensitive coatlng.

Fine powders of vari-ous types are suitable for the development of the latent image and these Vpowders also may be colored; examples are powdered inorganic and organic dyestuis, metal powders, glass powders and synthetic resin powders, of a particle size in the range of 0.1V to 100g, preferably 1 to 20M. The powders are used either alone or on a carrier. Suitable carriers are brushes of various types, rollers, particularly rollers tted with bristles or having a plush covering and also line glass or synthetic plastic balls having a particle size of a few hundred microns, or metal filings.

To develop the latent heat image and render it visible, the latent image is contacted for a short time with one of these powders, using a carrier if desired. The iine powder adheres to the image-bearing parts of the heatsensitive coating to form a visible imagel corresponding to The infra-redV the master. For most purposes, particularly if a synthetic resin powder is used, the visible image has sufficient resistance to smearing, but such resistance can be improved by fixing. Fixing can be effected by heating or by exposing the image to solvent vapor. Alternatively, a coating of lacquer or a transparent foil can be applied to the image.

By the process according to the invention well dened non-reversed positive or negative copies of high contrast and suitable for use as documents can be produced very simply from masters having text on one or both sides.

The invention will be further illustrated by reference to the following specific examples:

Example I A solution in 100 parts by volume of methanol of 7.5 parts by weight of methoxymethylated polyhexarnethylene diamine adipate, in which about 40% of the carbonamide hydrogen .atoms have been replaced by methoxymethyl groups, is mechanically coated upon paper, weighing grams/square meter, which has been'precoated to prevent penetration by organic solvents. The coating is dried with hot air at a temperature of to 100 C. An image is. produced on the dried coating in the following manner: the copying material is placed under a master and passed in close contact with the master by rollers at a speed of l0 meters a minute through the focal point of a focused l350-watt infra-red radiator.

To render visible the result latent image on the heatsensitive coating, the developer described below is scattered evenly over it. The dyestuif particles adhere to the heated parts of the coating, which correspond to the text of the mastenand a legible image of good contrast appears which is nearly smear-proof and usually does not require fixing. The developer consists of parts by Weight of glass balls of a particle size of 350-400p. and 2 parts by weight of .a colored resin powder of a particle size of 20-50g, made by melting together 30 parts by Weight of polystyrene, 30 parts by weight of a maleinate resin and 3 parts by weight of carbon black, the melt being afterwards ground and screened.

Example Il A waxed paper weighing 40 grams/square meter is mechanically coated on both sides with a solution in 100 parts by volume of 80% ethanol of 7,15 parts by weight of a methoxymethylated polycaprolactam, in which about 30% of lthe carbonamide hydrogen atoms have been replaced by methoxymethyl groups. The thickness of each coating is about 5h. The coatings are dried with hot air. To prepare a copy from a master with text Ion both sides, the copying material is placed against the side of the master which is to be `copied and the master is exposed (through the copying material) to infra-red radiation as described in Example I. A non-reversed latent image corresponding to the master is formed on the side of the copying material remote from the master. This image is rendered visible by treatment with a colored resin powder as described in Example I. lf a high degree of resistance to smearing is required `in the copy, the colored image can be fixed by a brief intensive further exposure to radiant heat. A copy suitable for use as a document is obtained. The copy has good contrast and can be used as an intermediate for further copying, for example by the diazotype process.

Example III A 7.5% solution in methanol of a methoxyrnethylated polycapr-olactam, yin which about 30% of the carbonamide hydrogen atoms have been replaced by methoxymethyl groups, is coated upon paper weighing 80 grams/ square meter which has been precoated to prevent penetration by organic solvents, the thickness of the coating being about 10p.. The coating is dried with hot air and an exposed, developed and fixed photographic lm is then placed, silver-side down, on the coating. A negative master `to be copied is then placed on top of the ilm and exposure to infra-red radiation is eected, as described in Example I, with the negative master facing the radiation source. Development of the latent image is performed in the manner described in Example I with a developer consisting of a pigmented resin powder and line glass balls. A clearly legible image, which Iis nega- .tive in relation to the master, is obtained.

Example IV Paper Weighing 8() grams/square meter, which has been precoated to solvent penetration by organic solvents, is coated with a 7.5% solution in methanol of a mixed condensation product obtained from 60% adipic acid and hexamethylene diamine and 40% caprolactam. After the coating has been dried with hot air, it has a thickness of about S-lOn. The coating is placed under a film master or a thin paper master and is subjected, in close Contact therewith, t-o a brief intensive exposure to intrared radiation. The latent heat image Athus formed is made visible by treatment with a pigmented powder as described in Example I.

Instead of using the mixed condensation product obtained from `adipic acid, hexamethylene diamine and caprolactam, a mixed condensation product from adipic acid and hexamethylene diamine, adipic acid and 4,4- d-iamino-diphenylmethane and caprolactam, condensed in the proportions 1:111, can be used with equal success.

Example V A solution of l5 parts 'by weight of a chlorinated polyvinyl chloride 4in l5() parts by volume of toluene and 50 parts by volume of butanol is mechanically coated upon paper Weighing 80 grams/square meter, which has been precoated to prevent penetration by organic solvents. After the coating has dried, it has a thickness of about 10p. The copying material is place-d on top of a typeW-ritten master and passed at a speed of a few meters a minute in front of an infra-red radiatior, close contact being maintained between the copying material and the master. A latent image corresponding to the master is produced on the heat-sensitive coating.

This image is made visible by treatment with the developer described in Example I. The resistance to smearing of the visible developed image is increased by xing it by a brief further exposure to radiant heat.

Example Vl Results which are the equivalent or" those obtained in Example V are obtained by the use of a heat-sensitive coating formed by dissolving 36 parts by weight of polystyrene and 7 parts by weight of tricresyl phosphate in 420 parts by volume of chlorobenzene Iand 180 parts by volume of toluene and applying this solution to the paper described in Example V. The heat-copying process is accomplished as described in Example V.

Example VII Paper as described in Example V is mechanically coated with .a solution of l parts by weight of a polyacrylic acid ester in l0() parts by volume of 1toluene to produce, after drying, a coating of thickness about -10u. The coating is given a brief exposure to intensive infra-red radiation through a master which is in intimate contact with the coating. lThe latent image is rendered visible as described in Example V.

Example VIII Instead of the polyacrylic acid ester used lin Example VII, a .polyester is used. This polyester is produced by esterication of a mixture of 60% terepllthalic acid and 40% of isophthalic acid with ethylene glycol. Otherwise the procedure is as in Example VI. The resultant copy has excellent contours.

6 Example IX l5 parts by weight of shellac are dissolved in 100 parts by volume of methanol and the solution is coated upon paper Weighing 110 grams/square meter which has been given a precoat to prevent penetration by organic solvents.

The coating is exposed and the image developed as described in Example V.

Instead of the shellac coating just described, a coating produced by the application and drying of a solution of 25 parts by weight of colophony in 100 parts by volume of toluene can be used with equal success.

Example X Example XI Paper Weighing 60 grams/ square meter, which has been provided by extrusion with a coating of polyethylene of a thickness of about 15p., is passed together with a transparent film master at a speed of several meters a minute through the focal point of a focused BSO-watt infra-red radiator, the master being maintained in intimate Contact with the polyethylene coating. The latent image is developed as described in Example I and fixed by a brief further exposure to heat.

Example XII yPaper weighing grams/square meter that has been precoated to protect it against penetration by organic solvents is mechanically coated with a solution of 25 parts by weight of `a ketone-formaldehyde resin, having a softening temperature of l15l20 C. and an acid number of O, in parts by volume of toluene. After drying, the coating has a thickness of about 5-l0,u. This coating, in intimate contact with a positive lm master, is exposed to brief intensive infra-red radiation. For this purpose, it is passed at a speed of a few meters a minu'te through the focal point of a focused 1350-Watt infra-red radiator. Close contact between the master and the copying material is ensured by two pressure rolls. The latent image is developed and fixed as described in Example I.

To increase the smear-resistance of the finished copy, it is subjected to a brief further exposure to heat. It can, for example, be passed through the apparatus in which the latent image was produced. With equal success, a solution of a formaldehyde-ketone resin, having a softening temperature of 76-82 C., can be used for the preparation of the heat-sensitive coating.

Example XIII A solution of 25 parts by weight of a maleinate resin, having a softening temperature of 15G-158 C. and an acid number of 20, in 100 parts by volume of toluene is mechanically coa-ted upon paper which has been pretreated to render it resistant to solvents. The resultant maleinate resin coating, the thickness of which is about 10p, is exposed, under a thin master, e.g. a typewritten air mail letter, to infra-red radiation in the manner described in Example XII. The latent image is developed as described in Example I. An easily legible high-contrast image corresponding to the master is obtained.

Instead of the maleinate resin having a softening ternperature of ISO-158 C., maleinate resins may be used having a softening temperature of 119 to 126 C. and an acid number of 10 to L1 or a softening temperature of 60 to 70 C. and an acid number of 120-130.

Example XIV 25 parts by Weight of a phenol-formaldehyde resin, having a softening temperature of 10S-118 C. and an acid-number of O, are dissolved in 100 parts by volume of butanone and the solution is coated upon a paper foil which has'been precoated to protect it from penetration by organic solvents. Exposure, development and xing are accomplished as described in Example X11.

Instead of the foregoingphenol-formaldehyde resin, a phenolic resin of the non-plasticized resol type can be used, eg. a product having a softening temperature of 45 to 58 C., the coating solution consisting of 15 parts by weight of this Vresin dissolved in 100 parts by volume of ethyl acetate.

Example XV 15-parts by weight. of a phenolic resin modified with colophony, and having `a softening point of 59-65 C. and an acid number of about 80, are dissolved in 100 parts by volume of ethyl acetate, and the solution is mechanically coated upon a paper support. Copies are prepared as described in Example XII.

A phenolic resin modified with colophony, :and having a softening temperature of Y1Z0-130" C. and an acid number of underr20, may be used with equal success.

It Will be obvious to those skilled in the art that many modifications may be made Within the scope of the present invention Without departing from the spirit thereof, andthe invention includes all such modifications.

What is claimed is:

1. A copying process which comprises:

(a) forming a latent heat image in a heat-softenable resin layer by exposing said layer and an adjacent master to radiant heat and (b) developing thelatentheatimage formed in said layer by contacting it with a. developer powder.

2. A process. according to claim 1 in which the developed image-is ixed.

3. A. process according to claim 1 in which the powder is colored.

4. A. process according to claim 1 in which the layer is self-supporting.

5. A process according to claim 1 in which the layer is supported.

6. Aprocess according to claim 1 in which the layer comprises a synthetic resin having a softening temperature in the range'of about 40 to 180 C.

7. A process according to claim 6 in which the resin is a polyamide.

3. A process according to claim 6 in which the'resin is a polymer of an w-aminocarboxylic acid.

'9. Aprocess according to claim 6 in which the resin lis a condensation product of a diamineand a dicarboxylic acid.

10. A process .according to claim 6 in which the resin A is a polycaprolactam.

11. A process according to claim 6 in which the resin is a condensation product of adipic acid and hexamethylene diamine.

12. A process according to claim 6 in which the resin is a mixed condensation product of adipic acid, hexarnethylene diamine, and caprolactarn.

13. A process according to claim 6 in which. the resin is a polyamide containing alkoxyrnethyl substituents on some of the carbonamide nitrogenratoms.

i4. A process according to claim 6 in which the resin is a methoxyrnethylated polyhexamethylene diamine adipate.

15. A process according to claim .6 in which the resin is a methoxyrnethylated polycaprolactam.

16. A process according to claim 6 in which the resin is a polyvinyl compound.

17. A process according to `claim 6 in which the resin is a polyester.

i8. A process according to claim 6 in which the resin is a polyoien.

19. A process according to .claim 6 in which the resin is a polyacrylic acid ester.

20. A process according to claim 6 in which the resin is a ketone-formaldehyde resin.

21. A process according toclaim 6 in which the resin is a maleinate resin.

22. A process according to claim 6 in which the resin is a phenol-formaldehyde resin.

Z3. A process according to claim-6 in which the resin is a phenolic resin modified with colophony.

24. A process according to claim 1 in which the layer comprises a natural resin having a softening temperature in the range of about 40-180 C.

25. A process according to claim 24 in which the resin is shellac.

26. A process according to claim 24 in which the resin is colophony.

27. A process according to claim l inwhich` theresin is a mixture of diand tetrahydroabietic acids.

References Cited by the'Examiner UNITED STATES PATENTS 2,297,691 1.0/42 Carlson 117--25 XR 2,561,513 7/51 Horback 117-25 2,616,961 11/52 Groak lOl-149.4 XR V2,847,330 8/58 Toulmin.

2,855,324 10/58 Van Dorn 117-17.5 XR 2,909,443 10/59 Wolinski 117-13 .XR 2,974,060 12/61 Dettling 117-21 3,060,024 10/62 Burg etal 96-115 3,081,699 3/63 Gulko 117-17 X 3,089,953 5/63 Lind et al. Z50-65.1 3,094,619 6/63 Grant 1117-36L8 FOREIGN PATENTS 806,677 12/58 Great Britain.

WTLLAM D. MARTN, Primary Examiner.

RICHARD D. NEVUS, MURRAY KATZ, Examiners. 

1. A COPYING PROCESS WHICH COMPRISES: (A) FORMING A LATENT HEAT IMAGE IN A HEAT-SOFTENABLE RESIN LAYER BY EXPOSING SAID LAYER AND AN ADJACENT MASTER TO RADIANT HEAT AND (B) DEVELOPING THE LATENT HEAT IMAGE FORMED IN SAID LAYER BY CONTACTING IT WITH A DEVELOPER POWDER. 